In inkjet printing, minute droplets of black, white or coloured ink are ejected in a controlled manner from one or more reservoirs or printing heads through narrow nozzles on to a substrate which is moving relative to the reservoirs. The ejected ink forms an image on the substrate. The resulting image should be as high quality as possible.
Inks which cure by the polymerisation of monomers may contain a wide variety of monofunctional, difunctional and multifunctional monomers. The challenge is to provide the necessary printing properties, whilst providing a high-quality image, without compromising the jetting properties. This is made all the harder in inks which are formulated without the use of water or volatile organic solvents (which also have their own disadvantages).
Inks based on monofunctional (meth)acrylate monomers tend to have excellent adhesion and low shrinkage, but generally have poor resistance properties (blocking, solvent resistance, etc). Also purely monofunctional (meth)acrylate monomer-based inks (and particularly those containing NVC), despite giving films with high elongation, suffer from poor embrittlement of the substrate. To boost the resistance properties it is necessary to include difunctional or multifunctional (meth)acrylate monomers to impart a degree of cross linking, but the addition of such components tends to lead to reduced adhesion.
There is therefore a need in the art for an inkjet ink that has the correct balance of adhesion, blocking resistance and low embrittlement.